Finger operable control device

ABSTRACT

A finger operable control device that includes a sensor having five conductive plates. The conductive plates are coupled to a detector circuit arranged to sense capacity imbalance due to the presence of a finger or an earthed object on or by one or more of the conductive plates. The device is utilized as a mouse or joystick.

FIELD OF THE INVENTION

The present invention relates to finger-operable control devices forcontrolling equipment such as computers or position-controlled devicesand the like.

BACKGROUND INFORMATION

Control devices such as mouse, trackball, or joystick are used tocontrol such equipment but all these have moving parts and in the caseof a mouse a level table surface is needed. Joysticks and trackballs arebulky and require robust mounts and all are protrusive. Touch-plateswitches are known, but these are simple on/off devices.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a finger-operablecontrol device having at least some of the following characteristics,that is a device which:

a) is compact,

b) has no moving parts,

c) can be conveniently mounted on an instrument panel,

d) can be operated on an uneven surface,

e) can be sealed against dust, moisture or liquid,

f) is not affected by vibration,

g) has a control response which is extremely fast and not subject tosubstantial lag between operation by the operator and response by theinstrument.

According to the present invention a finger operable control device(such as a joystick emulator or mouse) comprises a sensor having acentral electrically conductive plate, a first pair of electricallyconductive plates on a first axis and spaced from opposite edges of thecentral plate to form a first pair of capacitors therewith havingsubstantially equal capacitance, a second pair of electricallyconductive plates on a second axis different from the first and spacedfrom opposite edges of the central plate to form a second pair ofcapacitors therewith having substantially equal capacitance and ischaracterised in that at least one of the plates is connected to adetector circuit arranged to sense capacity imbalance between at leastthe first pair of capacitors induced by the presence of a finger orfinger operable earthed object placed on or near the conductive plateswhen the finger or object is disposed asymmetrically along the firstaxis with respect to the central plate.

The plates may be formed as a matrix of copper conductors on a printedcircuit board. In some embodiments of the invention one or more of saidconductive plates may be driven by alternating signals, and in others,the plates are connected to phase-sensitive detectors.

The amount of signal detected is normally small, being due to straycapacity between conductors of the matrix which is balanced by design togive a very low zero residual signal. The presence of a grounded objectsuch as the operator's fingertip intercepts some of the electrical fluxand unbalances the stray signals. The phase and amplitude of theimbalance depends on the precise position of the fingertip, i.e.,whether it is to the left or right of the axis of symmetry of thematrix, or above or below the centre-line. Sensitivity to angulardirection and distance of finger movement is determined by the design ofthe matrix.

The detector output is passed to logic circuits which convert the outputinto a form suitable for transmission to a computer or other indicatingdevice so as to control for example the position of a cursor on adisplay screen by slightly varying the position of the operator's fingerlocated on the sensitive area of the device.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of examplewith reference to the accompanying drawings, in which;

FIGS. 1A-F show five embodiments of a sensor matrix,

FIGS. 2A-C show a perspective, a cross-section on line B--B of FIG. 1Aand a side view of a device according to the invention,

FIGS. 2D and E show a side cross-section and an elevation of a devicesimilar to that of FIGS. 2A-C according to the invention.

FIG. 3a shows a single-axis device with a balanced drive and anunbalanced detector,

FIG. 3b shows a single axis device with the drive applied to the centralplate and a balanced detector coupled to the other plates,

FIG. 3c shows a 2-axis sensor with a quadrature squarewave drive andphase sensitive detectors using D-registers,

FIG. 4 shows a joystick emulator embodying a device according to theinvention.

FIG. 5 shows a Quadrature-Mouse emulator embodying a device according tothe invention,

FIG. 6 shows a combined Joystick/Mouse emulator embodying a deviceaccording to the invention.

In the drawings, like parts are given like references.

DESCRIPTION OF PREFERRED EMBODIMENT

FIGS. 1A to 1E show a number of possible configurations of a sensoraccording to the invention, where FIG. 1A and FIG. 1B depict single-axissensors 10a/10b comprising two conductive plates 11a/11b, 12a/12barranged symmetrically about a central plate 13a/13b. FIGS. 1C, 1D and1E depict 2-axis sensors 14c/14d/14e having four plates 15c/15d/15e to18c/18d/18e arranged symmetrically about a central plate 19c/19d/19e.FIG. 1F shows a preferred configuration.

The sensor matrix 10, 14 is conveniently formed by normal printedcircuit techniques. Since a human finger-tip makes a near-circularcontact of about 1 cm diameter, the central electrode 13, 19 ispreferably made circular and about the same size, anything largercalling for an undue movement before any response is achieved, andanything smaller reducing the available output of the device.

In the preferred arrangement of FIG. 1F the four outer electrodes 15 to18 form equal segments equally spaced from the centre electrode 19, thespace being approximately equal to the thickness of the insulatingsubstrate which separates the finger from the electrodes, greaterspacing reducing the effective capacitance and therefore the availablesignal, and less spacing reducing the amount of capacitance which can beintercepted by the finger.

The single connection 20 from the sensor central electrode 19 and theamplifier (or the drive), to be described inevitably runs close to theconnection leads to two of the outer electrodes. To neutralise, or atleast substantially reduce the resultant unbalance of the sensor, thecentral electrode has a dummy lead 20' extending diametrically oppositeto the amplifier lead 20, and of sufficient length to provide acounterbalancing stray capacitance to the other two outer electrodes.Connections to all electrodes are printed so as to present a stable andwell defined stray capacitance to the amplifier leads.

Similar extensions to the central electrode are printed at right anglesto the earlier pair in order to maintain the same response to fingermovement in all four intermediate directions, NE,SE,SW,NW.

This lead balance is non-critical when the leads are remote from theamplifier input connection or when they are screened by interveninggrounded area of the printed circuit board.

To give overall screening and to reduce the influence of hand movementremote from the sensor, the external side of the pcb is copper-clad,with holes positioned accurately over each sensor. The underside of thesensor can be either screened or stood-off from the case or externalobjects by a distance much greater than the pcb thickness, so as toavoid influence from the position of external objects. In either case nomovement of objects immediately behind the sensor should be allowed,neither conductors nor di-electrics.

FIG. 2 shows in simplified outline a typical embodiment of a device 22according to the invention. A double-sided printed-circuit board 24forms the top of a shallow enclosure 26. The upper surface 24a of 24 isa ground-plane with circular apertures 24b, 24c in the copper whichcoincide with the location of two sensors 14, which are printed on theunderside of the pcb. The underside also carries the circuitry tosurface-mounted IC's 28. A nine-conductor cable 30 connects the outputof the device 22 to a host computer (not shown). The overall size of thedevice 22 is typically 160 by 80 by 7 mm.

A modification of the device 22 shown in FIGS. 2A to 2C is shown inFIGS. 2D and E at 122. This device 122 comprises a panel 124 made fromplastics or other suitable dielectric material about 1.5 mm thick. Acircular depression 125 indicates the location of the active area of thesensor and a thicker rim 126 around the depression strengthening thepanel in this area. A flexible printed circuit board (p.c.b.) 127 ismounted by means of a metal rivet 128 under the panel. The p.c.b. hasformed on it four outer electrodes 15 to 18 equally spaced from acentral electrode 19 as is shown in FIG. 2E. The head 129 of the rivet128 and the rivet itself is insulated from the central electrode andacts instead of the upper surface 24 of the previous embodiment as aground plane contact. The head 129 of the rivet not only acts as aground contact but provides a sensor locating and retaining stud and atactile point to assist the finger in finding the neutral point of thesensor.

The device 122 can be mounted directly to the inside face of a computershell in suitable proximity to certain keys of the computer keyboard,one or more such keys being used as the fast/slow control andclick-buttons in place of a second finger-sensor. The complete assemblyof the device need be little larger than the sensor area itself which islittle more than 25 mm square.

Balanced output can be achieved either by driving from a squarewavegenerator 32 the central electrode 13 or 19 and using a balanced-inputamplifier 34 which will respond to the difference of the two outputs onouter electrodes 11, 12 as in FIG. 3b or preferably by driving the outerelectrodes 11, 12 in balanced antiphase fashion and using an unbalancedamplifier 36 as in FIG. 3a, since the amplifier 36 now sees only thedifference signal which being smaller is much easier to handle, and thegeneration of anti-phase signals is a trivial task, especially ifsquarewave signals are used.

In order to give full directional signals the two-axis arrangement ofFIG. 3c can be used where the horizontal 16, 18 and vertical 15, 17pairs of electrodes are driven in phase-quadrature by square-waves.Registers D1 and D2 provide balanced antiphase outputs at half thefrequency of oscillator 32, the output of D2 being one half-perioddelayed on D1 by the action of inverter N1.

The separate contributions of vertical and horizontal output from thesensor 14 are resolved by registers D3 and D4 which act asphase-sensitive detectors, each being clocked in synchronism with theappropriate drive signal.

It is convenient but no essential to couple the central electrode 19 tothe registers D3, D4 by way of an "operational amplifier" 36 with a lowbandwidth such that it acts as an integrator. Since the drive signalsare conveniently squarewaves, the imbalance signal will be composed ofsquarewaves, and the output of such an amplifier 36 will be a series oframps, reaching maximum or minimum values at the end of each half-periodof the squarewave.

These maxima will be synchronous with the clock pulse applied to thecorresponding "phase-sensitive" D-register. Thus the register will latchand give a TRUE output at the Q terminal only if the ramp issufficiently positive at the instant the clock terminal goes positive.

An important feature of this ramp output from the amplifier is that itslevel corresponds exactly with its mean level at the intermediate clockintervals, thus those registers clocked by quadrature signals will notrespond, except to finger movement in an orthogonal direction. Movementin an intermediate direction will give an output from TWO registers.

The physical orthogonality of the sensor 14 is linked to the phaseorthogonality of the sensors' quadrature drive signals and it isdesirable that the latter be truly orthogonal, i.e., that they beexactly in phase quadrature. This is achieved if the clock generator hasunity mark-space ratio, which itself can be achieved by running theclock at twice the desired output frequency then using a divide-by-twocircuit as in FIG. 6.

In order to ensure that no response is provided by the device unlessdemanded, despite noise, drift, and offset errors, a "deadzone" shouldbe built into the system, such that a finite displacement of the fingerfrom its central, neutral position is necessary to cause a response. Thedeadzone may be dispensed with if the finger is in constant contact andthe ultimate sensitivity is desired.

This deadzone is readily achieved by biasing the amplifiers to a levelof say 0.25 volts lower than the threshold of the phase-sensitivedetectors, 0.25 volts being about half the maximum output available fromthe sensor. See FIG. 4. The threshold of the CMOS D-registers which formthe phase-sensitive detectors is typically Vd/2+/-5%, so the bias shouldbe Vd/2-5%-0.25 v. This is achieved by resistor chain R3,R6,R7.Reduction of the deadzone can be controlled by a second sensor (notshown), one of whose phase-sensitive detector outputs is applied to theR4 terminal labelled "Fast".

Referring to FIG. 6, if a comparator 38 is interposed between theamplifier A1 and phase-sensitive detector D3 to D6 then the +/-5%uncertainty is diminished by the effective voltage gain of thecomparator and may be ignored. In this case a series string of threeresistors, 40, 42, 44 of say 0.1 megohm, 0.01 megohm, 0.1 megohm willprovide two voltages, one at V/2-V/42 for the comparator and the otherat V/2-V/42 for the amplifier. The amplifier is configured to give unitygain at DC so the other comparator input will be at this same voltageand the effective bias will be equal to 2 V/42=0.24 volts approximately.

Whereas a significant deadzone as previously described may be desirablefor the "button" outputs, the directional outputs should preferably givea linear response. This can be achieved by superimposing on the deadzonebias an alternating signal such as random noise or preferably a ramp ofpeak amplitude just less than the deadzone voltage. A suitable ramp canbe derived from a squarewave as in FIG. 5 or FIG. 6 where the outputfrom a suitable squarewave source 46 is converted to a ramp by a seriesresistor 48 and shunt capacitor 50.

Those outputs which are equivalent to "button-presses" should have aminimum output pulse-width to simulate a mechanical switch withbacklash. This may be achieved by using the normal phase-sensitivedetector output to operate a latch which can only change after a definedinterval. FIG. 6 shows such a way, where D17-20 are clocked at a slowspeed and will follow the phase-sensitive detector outputs only if thelatter are sustained for a finite time, and will hold that output for atleast 1 period of the slow clock.

In order to properly emulate a quadrature mouse, the directional outputshould produce two sequences of pulses in phase-quadrature, for eachdirection of movement left-right and up-down. These can be produced asshown in FIG. 5 where registers D9, D10 form a quadrature generatorproducing squarewave outputs at OA1, OB1 which are in phase quadrature,the leading output being determined by the Up/not Up control input toExclusive-OR gates X1,X2 which reverse the sense of feedback to the tworegisters. The maximum possible rate of change of the output squarewavesis determined by the pulse rate of the "mouse clock" applied to D7 whichis selected from the outputs available from the frequency divider FD1 bythe action of gates N3,4,5 under the control of the output from the F4button, not shown. The actual transitions of the output squarewaves atOA1 and OB1 are regulated by the NOT outputs of the UP or DOWN registersD3, D4 via gates N6, N8. Left/Right quadrature signals at OA2, OB2 aregenerated in similar fashion.

In the following description of FIG. 6 the following devices may beused:

D-registers can be type CA4013 from RCA and others, NAND gates can be1/4 of CA4011 from RCA and others, XOR gates can be 1/4 of CA4070 fromRCA and others.

All can be part of an ASIC from various sources, except perhaps theamplifiers which are preferably type TLC251 from Texas Instruments.

The following terms are used:

Joystick: a device resembling the control column of an early aircraft,which has four switch contacts the appropriate one of which is closedwhile the stick is held forward, backward, left, right. It may also haveswitches which are closed by "Fire" buttons mounted on the stick or onits base.

Mouse: a device which is pushed across a surface to give signalsaccording to the direction of motion. The Mouse usually also containsbutton-operated switches and may produce signals similar to those of aJoystick. Some sophisticated Mouses are also capable of emulating any ofthe following:

Quadrature Mouse: a mouse which generates two sets of signals, one foreach direction of movement forward/backward and left/right, each setcomprising pulses on two separate lines, these pulses being inphase-quadrature. Distance moved is indicated by the number of pulses orby the number of transitions of the quadrature signals, and direction bythe relative phase of the signals.

Serial Mouse: a Mouse whose signals are transmitted to the computer viaan RS232 or other serial link.

Bus Mouse: a Mouse whose signals are transmitted in parallel-datafashion over more than one line, usually to a special hardware decodingdevice within the computer.

Open Drain: a CMOS logic element whose output terminal shows either alow resistance to ground, Logic True=active low, or is virtuallyopen-circuit. Logic False=off or floating. Equivalent to a TTL opencollector element.

ASIC: Application-specific Integrated Circuit.

UART: Universal Asynchronous Receiver and Transmitter.

N1, N3 form an oscillar of approximately 32 kHz frequency which drives adivide-by-two circuit 52 formed by register D0 whose antiphase outputsdrive registers D1, D2 which form a quadrature-phase generator whichdrives the two finger-sensors 14a, 14b.

The output from sensor 14b is amplified and integrated by integratingoperational amplifier A2 which drives a comparator C2 which drives theData input terminals of the four registers D13-D16 which act asphase-sensitive detectors. The second input of the comparator C2 is atthe Vref potential which is Vdeadzone higher than the output of theamplifier, so that only signals greater than Vdeadzone will produce anoutput.

Each detector output is captured and held by the following register setD17-D20 which are clocked at a slow speed, perhaps 5 Hz, thus producinglong pulses which simulate a mechanical switch without contact bounce.These outputs drive the "open-drain" output elements Od1-Od4 thus givingeffective "contact-closure-to-ground". These simulate the Fire-buttonoutputs of a Joystick, or the Click buttons of a Mouse.

Sensor 14a similarly drives four phase-sensitive detectors D3-D6 via anamplifier A1 and comparator 38 but now the deadzone is filled by theramp-signal generated by a 5 Hz squarewave and the action of the 10Megohm resistor 48 and 0.1 microfarad capacitor 50 at the non-invertinginput of A1. The 5 Hz signal driving this network can be turned off highor off low by additional logic or by initialisation signals in order togive either zero deadzone, maximum deadzone, or linearising ramp.

For Joystick emulation the outputs of the phase-sensitive detectorsD3-D6 are applied to the "open drain" elements Od5-Od8 via multiplexinglogic not shown. For Quadrature Mouse emulation the detector, NotQoutputs of D3,D4 are used to gate clock pulses into D7 which receivesthe slower "mouse clock" pulses as Data input. The slowly-changingoutputs of D7 drive the quadrature generator formed by D9,D10 whosephase sequence is controlled by the Up/Not Up signal into Exclusive-ORgates X1,X2 which act to reverse the sense of feedback in the D9,D10quadrature generator. The quadrature squarewaves are output at terminalsOA1,OB1 representing vertical motion. Quadrature generator registersD11,D12 are similarly controlled, outputting squarewaves to terminalsOA2, OB2 representing horizontal motion.

A change-over from Joystick to Mouse emulation can be effected byadditional logic (not shown), the detailed means of achieving this beinggoverned by the pre-setting capabilities of any ASIC into which thedesign may be incorporated.

Bus Mouse emulation can be achieved by outputting the pulses from D7 andD8 into 8 bit counters whose outputs are multiplexed onto an 8 bit busin known fashion.

Serial Mouse emulation can be achieved by multiplexing the output ofsuch counters via a UART and RS232 IC in known fashion.

The output from D14 can be used to control via gates N5, N6, N7 theselection of pulse-rate applied to D7 and D8 which sets the effectivespeed of movement of the Mouse emulation. The same output can be used tocontrol the magnitude of deadzone in the Joystick emulation by gatingthe 5 Hz ramp signal as already described.

The comparators are incorporated because of uncertainty of operation ofthe D-registers which may be part of an ASIC and not elements which canbe separately tested and adjusted.

I claim:
 1. A finger operable control device comprising a sensor havinga central electrically conductive plate, a first pair of electricallyconductive plates on a first axis and spaced from opposite edges of thecentral plate to form a first pair of capacitors therewith havingsubstantially equal capacitance, a second pair of electricallyconductive plates on a second axis different from the first axis andspaced from opposite edges of the central plate to form a second pair ofcapacitors therewith having substantially equal capacitance,characterised in that opposite members of each pair of plates are drivenby antiphase outputs of a quadrature-phase generator and the centralplate is connected to a detector capable of sensing the magnitude and/orphase of the signal therefrom caused by capacitive imbalance induced bypresence of either a finger or a finger-operable earthed object placedon or near the conductive plates when the finger or object is displacedlaterally from the intersection of the two axes.
 2. A device as claimedin claim 1 wherein the generator includes an oscillator operative at afrequency of twice the frequency of the quadrature phase signals.
 3. Adevice as claimed in claim 1 wherein the detector is preceded by anamplifier.
 4. A device as claimed in claim 3 wherein a dead-zone isprovided by appropriately biassing the amplifier.
 5. A device as claimedin claim 3 wherein a dead-zone is provided by connecting the output ofthe amplifier to a comparator, the second input of the comparator beingconnected to a reference signal to provide the dead-zone.
 6. A device asclaimed in claim 1 wherein the detector circuit comprises at least onephase sensitive detector having reference input coupled to an output ofthe first quadrature phase generator.
 7. A device as claimed in claim 6wherein the output of the phase sensitive detector is coupled to aninput of a second quadrature phase generator.
 8. A device as claimed inclaim 7 wherein a clock pulsing means is coupled between said phasesensitive detector and said second generator.
 9. A device as claimed inclaim 6, wherein said phase sensitive detector produces at its output asignal indicating displacement of the finger or object relative to atleast the first axis.
 10. A device as claimed in claim 4 or 5 whereinthe amplifier is biassed to a level lower than the threshold of thephase sensitive detectors, and wherein a ramp is applied to theamplifier bias whereby the dead-zone is at least partially eliminated.11. A device as claimed in claim 4 or claim 5 wherein a random noisesignal is applied to the amplifier whereby the dead-zone is at leastpartially eliminated.
 12. A device as claimed in claim 1 wherein anelectrical lead extends from the central plate between a plate of thefirst pair and a plate of the second pair, and a dummy lead extendsbetween the other plates of the first and second pairs.
 13. A deviceclaimed in claim 1 comprising at least two said sensors.
 14. A mouseemulator comprising a finger operable device as claimed in claim
 1. 15.A joystick emulator comprising a finger operable device as claimed inclaim 1.